1. Technical Field
The present disclosure relates to a packaged device exposed to environmental air and liquids and to the manufacturing method thereof. In particular, the present disclosure finds advantageous application in micro-electromechanical devices (MEMS), such as sensors made in semiconductor material chips provided with a sensitive area. For example, the disclosure may be used in pressure sensors, gas sensors, microphones and the like, which are designed to be exposed to environmental air for their operation but benefit from a barrier towards water or other liquids, for example water contained in droplets in the environmental air but also masses of liquids in which the device may be immersed by mistake.
2. Description of the Related Art
As is known, in certain applications, functionality of MEMS devices may be impaired or in any case limited in the presence of moisture. In fact, droplets of water may be adsorbed by the material of the devices, which consequently may swell, generating mechanical and/or electrical stresses, may modify their electrical characteristics (for example, sensitivity) with consequent erroneous readings, may be subjected to short-circuits that prevent their operation, or may even undergo damage, for example owing to corrosion of parts. In all these cases, the device becomes unreliable or even unusable.
For this purpose, also for reasons of mechanical protection, in certain applications MEMS devices are provided with protective caps that surround and protect from the external environmental each device and/or group of devices fixed to a common base.
In some known solutions, the protective cap is made of a completely impermeable material and is bonded or welded to the base to which the MEMS is fixed or on which it is printed. However, this solution is not always applicable. In fact, in certain applications, the sensor (for example, an atmospheric-pressure sensor) must be exposed to the external environment, so that it is not possible to use a cap impermeable to air.
When the MEMS device has to be in direct contact with the external environment, it is possible to provide holes in the cap; however, these form vias for diffusing liquids, such as water, condensed vapor, oil, flux used during welding of the MEMS on the electronic cards or other liquids which then may come into contact with the MEMS.
On the other hand, MEMS devices have to meet specifications that are increasingly stringent as regards the resistance to water and other liquids. For example, in cell phones of an advanced type, provided with barometric functions, it is desired to maintain functionality even when they are dropped into water to a depth of two meters for half an hour, in case of rain, or in case of splashes caused by waves. Similar specifications are called for by devices provided with Global Systems for Mobile Communication (GSM) with measurement of the axis Z. In washing machines, it has been proposed to use water-level sensors, which thus should be able to withstand hot vapors. Clocks having a depth measurement function and thus operating underwater, should be able to function properly.